Photographic speed monitor



March 8, 1960 s. X. SHORE 2,927,836

PHOT OGRAPHIC SPEED MONITOR Filed May 29. 1953 3 Sheets-Sheet 1REA/ZOFCAR OETECTOR lab 1 /7A /777/I LF il I vzaa 3m I L- J /36 INVENTORSIDNEY x. SHORE 4 i 12 g ATTORNEY March 8, 1960 s. x. SHORE 2,927,836

PHOTOGRAPHIC SPEED MONITOR Filed May 29. 1953 3 Sheets-Sheet 2 TIMER(ml/119M515 5 FUPFLOP) INVENTOR SIDNEY X. SHORE BY ATTORNEY March 8,1960 s; x. SHORE 2,927,836

PHOTOGRAPHIC SPEED MONITOR Filed lay 29, 1953 3 Sheets-Sheet 3 INVENTORSIDNEY X. SHORE ATTORNEY United States Patent 2,927,836 PI IOTOGRAPHICSPEED MONITOR Sidney X. Shore, East Rockaway, N.Y.

T 7 Application May 29, 1953,Serial No. 358,233 I 21 Claims. (Cl.346-107) The present invention relates to methods and apparatus formeasuring the speed of vehicles and photographing vehicles passing thedetection point at excess speed.

Various devices intended to accomplish this purpose have been devisedheretofore, involving doppler radar for speed measurement aswell aspneumatically or mechanically or photoelectrically operated switches atspaced points along a traific lane. So far as I am aware, all of thesesystems are deficient for photographing the speeder for several reasons.Theyare poorly adapted to the use of electronic flash lighting, which ishighly desirable if stop-motion sharp pictures are to be obtainedthroughout a Wide range of-change in natural lighting conditions. As apractical consideration in the use of electronic flash or strobelighting, as this form of photographic lighting has come to be known,the lighting must be aimed in such direction as to avoid blinding thedriver of the vehicle being photographed. A second requirement is thatthe strobe illumination should be consistently at a point as close aspossible to the vehicle being photographed in order that the lightingmay be intense and in order that the lighting may be confined to theimmediate region of the vehicle to be photographed so as not to extend,uncontrolled, to other traflic lanes where drivers might be blindedthereby;

The present invention provides a practical speed detection andphotographic system wherein strobe lighting may be used at short rangewith reliance that the vehicle to be photographed will invariablypresent its license plate at the particular restricted region where thestrobe light ing is effective. This is accomplished advantageously byemploying the highly localized forms of vehicle detectors that areembodied in minimum-elapsed-time speed measuring devices, suchaspneumatic tube actuated switches,

ice

speeding vehicle close to that one being photographed.

The system is not seriously defective however if it should photographthe front end or the center of a speeding vehicle without recording thelicense plate since this represents only the waste of a film and anomisslon by the detection system. An innocent driver is not atfected bysuch misoperation, and the fact that an, occasional speeder may escapedetection is of little consequence when it is realized that the presentspeed detection practice as conducted by patrolmen can apprehend only asmall percentage of speed-law violators.

With the foregoing in view, the present invention provides various formsof speed detector, and camera combinations which are responsive to therear of the vehicle being paced. In one type, the speed detector isdisahled until the rear of the vehicle has passed a point close to thespeed measurement apparatus. Of this type, 'one form disclosed in detailbelow involves equalizing the counts of wheels passing a first detectionpoint and wheels passing the first element of an elapsed-time form ofspeed measuring system. A second form disables the speedmeasuring deviceWhile all except the rear end of the I vehicie passes thespeed-measuring region. This form photocells, and the like, in a systemwhich responds to the rear end of a vehicle, rather than to the frontend or an uncertain portion of the vehicle as has characterized othersystems that I have heard of. It is accordingly feasible in this newsystem to photograph the rear of a vehicle which may be illuminated by adownwardly sloping strobe beam directed at the rear of the vehicle. Thisdirection of the beam is best suited to safe use of strobe lighting. Toachieve this therear of the vehicle is to control the processirrespective of whether the vehicle involved is short or very long, andwhether it has two axles as in pleasure cars, or three or more axles asin the case of trucks and trailer trucks.

The foregoing system has the advantage that, even i. apart fromstrobe'lighting, the rears of speeding vehi -cles may be photographed soas to record the license plates which are invariably carried at the rearof vehicles, where only in certain states are the vehicles equipped withfront license plates. 4

The systems involved are intended to function as reliable and automaticsubstitutes for traiiic patrolmen and for this reason should be asperfect aspossible in order that one vehicle that is proceeding --withinlegal limits may-not be photographed asthe result of detection of arenders the speed-measuring equipment effective after the rear of thevehicle passes a predetermined point. T h s second form has the featurein common with athird form disclosed below in detail, in that themeasurern nt Qf speed can commence as soon as the rear of the ve icl 'epasses a certain point in the traffic lane. In this third system, aunitary detector of therear of the vehicleserves also as a firstdetector of a speed-measuring combination. In the fourth system, thespeed measurement is initiated by the vehicle and is not suppressed bythe rearof-thevehicle detector, but that detector is effective by virtueof storage or holding means to act jointly with the speed measuringmeans to trip the camera.

The nature of the invention and its various further features of noveltyand their advantages will be best appreciated from the followingdetailed description of three illustrative but highly effectiveembodiments theteof, which are shown in the accompanying drawings.Inthes e drawings:

Figures 1, 2, 3, and 4 are combined wiring diagrams and schematicrepresentations of four different embodiments.

In Figure I, a vehicle 10 is illustrated travelling along a trafiic lane12 across which are stretched three pneumatic hoses 14, 16 and 18. Ifmultiple trafiic lanesare found side by side, it would probablybeexpedient to confine the hoses to a single traflic lane and to employ aduplicate system foreach of the adjacent lanes. Hoses I6 and 18 arenearer to each other than the minimum spacing between succession Wheelsof usual cars and trucks. A camera 20 is provided, convenientlysupported as on a lighting pole at the edge of the road or by any othersuitable means, with the camera trained verting stored electricalcharge, as of the order of 55), watt-seconds, in a flash commonly lessinduration than of a second. The carnera andthe strobe lighting unit aresynchronized by'hnown means, commonlylby utilizing contacts in thecamera shutter mechanism which fire the strobe unit at the instant thatthe shutter is fully open. Strobe unit 22 includes thestrobe lamp 22atogether with a reflector 22b; and it further advantageouslyincludes alouver 220 for confining the light beamto the region where the licenseplate 1,031 (many vehicle actuatingthe tube 18 might be located without,

however, allowing stray light to reach oncoming traffic. Camera 20 is ofany desired construction, advantageously incorporating automatic filmadvancing mechanism and incorporating auxiliary devices for recordingdate, time, location and speed. The camera employs an electromechanicalactuator 20a that is eliective to trip the shutter instantaneously andinitiate the film feeding cycle.

Hoses or pneumatic tubes 14 and 16 act together to initiate the speedmeasuring process which is completed under control of hose 18. Ina sensehose 14 is a rearof-the-vehicle detector, or simply rear detector" andhose 16 is a first speed measuring detector.

Each of the hoses is pneumatically coupled to a pair ofpressure-actuated contacts 14a, 16a and 18a, respectively, in a mannerwell known and accordingly not described in detail here.

Each of these contacts has a power supply 14b, 16b and 18b whichenergizes a related solenoid 14c and 16c in the first two instances; andsupply 18b energizes electro-mechanical actuator 20a of the camera atappropriate times.

Solenoids 14c and 160 include step switches with fixed contacts 14d ofwhich six are illustrated, and each step switch includes a movingcontact 14c that is advanced stepwise by the solenoid 14c. Solenoid 16csimilarly actuates a step switch having fixed contacts 16d, the same innumber as contacts 14d and the moving contact 160.

Between contacts 14:: and 16e there is connected a voltage source 24, acapacitor 26 and a resistor 28, in series. This series circuit iscompleted when moving contacts 14c and 16s are in like positions so asto be interconnected by a wire 30. One such wire interconnects eachfixed contact 14d with a corresponding fixed contact 16d. A resistor 32shunts condenser 26.

In operation there is a steady potential at junction 34 where condenser26 is connected to resistor 28. This is a small voltage where resistor32 is large relative to resistor 28. When the front wheels of a vehicleengage hose 14, contacts 14a are closed and moving contact 14e isadvanced one step to the next fixed contact 1411 and the next wire 30.At this time the charge in condenser 26 starts draining through resistor32. Hoses 14 and 16 are spaced sufliciently, as 20 feet for example, sothat the next wheels of the approaching vehicle pass hose 14 before thefirst pair of wheels reach hose 16. If there are three axles (as in alarge truck) hoses 14 and 16 are separated farther apart than thegreatest separation between any successive pair fo axles. Accordingly,

contact 14c advances once more before the first wheels reach hose 16.Ultimately the vehicle wheels cause contact 16a to advance the samenumber of steps as contact 14c; and when this happens, the seriescircuit described is completed. Momentarily the voltage of directcurrent source 24 is transmitted via condenser 26 and is largelyimpressed on resistor 28; but this decays as condenser 26 becomescharged. By this process a sharp pulse is developed across resistor 28,at junction 34 with respect to contact 16a.

In the foregoing process, hose 14 acts to count axles or pairs of wheelsand hose 16 (with its associated apparatus) counts similarly, the countsof the first hose being equalized with the counts of the second hoseonly when the last pair of wheels has actuated hose 16. The equalizingprocess is one of equal addition or of subtraction, depending on onespoint of view.

It will be evident to those skilled in the art that theelectro-mechanical counters 14c, 14d, 14s and 16c, 16d, 16e may bereplaced by other well-known forms of counters such as the vacuum tubeor gas tube ring counter; and the counters employed may utilize anyconvenient number of counter positions. Suitable means (not shown) maybe provided for insuring that the counters are zeroed or set tocorresponding positions than when they are at rest; and with equivalentelectronic ring counters, the zeroing operation is accomplished readilyas is well known.

the vehicle.

When the same number of wheels has passed hose 16 as previously passedhose 14, a pulse is developed at point 34 that initiates the start of atiming operation. This may be accomplished in a wide variety ofelectromechanical and electronic ways. The following is an etiectiveillustrative embodiment. Rectangle 36 represents a timer. This rectangleencloses a monostable flipfiop of well known design as is described involume 21 of the Radiation Laboratory Series published in 1948 byMcGraw-Hill, at pages 591 and 592. Briefly, this timer incorporates apair of vacuum triodes 38 and 48. Each triode has its own load 38a, 40awhere load 4011 conveniently is in the form of a relay whose contacts 4%are open so long as the relay is energized. These triodes have a commonbias resistor 39 so that current passed by one triode reflects bias intothe other. Triode 40 has its grid operating normally at a high positivepoten tial, derived through resistor 40c that is connected to B-plus.The control grid of triode 38 has a bias that is fixed at a suitablevalue by voltage divider 38b, 38c that is connected between B-plus andB-minus. A condenser 42 furnishes cross-coupling between the anode oftriode 38 and the grid of triode 40.- The values of resistor 40c andcondenser 42 are chosen to provide the right time interval between theinitiating input pulse and the end of the timing pulse generated by theflip-flop. This operation is as follows:

In normal operation triode 40 conducts amply to energize relay 40a andopen contacts 40b, and thiscurrent provides bias across resistor 39 thatexceeds the drop across section 380 of the voltage divider sufficientlyto drive triode 38 well into cutoff. When a negative pulse istransmitted from junction 34 through condenser 44, that negative pulseinitially is transmitted to the grid of tube 4t), which tube isimmediately cut off, and the charge thus developed in condenser 42 musttake time before it has discharged through resistor 40c sutiiciently toallow tube 40 to conduct again. This involves substantial time and theeffect is sudden because, so long as tube 40 is cut off, tube 38 isconductive and develops grid bias for tube 40 in resistor 39.

During the operation of the monostable flip-flop 36 relay contacts 40bremain open. This time is determined by almost all of the valuesemployed in the flip-flop. This time interval is chosen so that a set ofrear wheels passing hose 16 will fail to reach hose 18 for any vehiclespeed up to the legal limit. Thus for a speed of 60 miles per hour or 88feet per second, and for a spacing between hoses 16 and 18 of four feet,the contacts 48!) will remain closed for approximately /22 of a second.

If a vehicle should traverse the hoses 16 and 18 in less than the timeinterval for which contacts 4% are closed, a circuit is completedbetween contacts 48b, 18a and camera tripper 20a. This circuit isenergized by supply 18b, to trip camera 20 and photograph the rear ofvehicle 10 including license plate 18a, with the aid or" theillumination from synchronized strobe lighting unit 22.

It is significant that in this system the operation of the timingapparatus under control of contacts 16 and 18 is suppressed until therear wheels of the vehicle to be photographed reach hose 16 andconsequently the rear of the vehicle will be in position to bephotographed if the vehicle has exceeded the time interval permissible.The precision of the location of trippers 16 and 18 is excellent so thatthe camera can reliably be counted on to frame the rear of the vehicleaccurately. However, if by some mischance hose 16 should initiate thetiming cycle before the rear wheels have passed, e.g. under control ofsome other set of wheels forward of those rear wheels, the consequencewould be to photograph some middle portion of Such misoperation isentirely unexpected; but even if it should occur, there is no penaltyimposed on an innocent driver and the only result is the inconsequentialescape and failure of detection of a speeder.

Ordinarily there will be no reliable rep at operation of i-to makecontact by vehicle-wheel pressure.

{he-camera in response to each set of wheels because of severallimitations. Itis desirable that timer 36 may relia'b'lyeesume itssteady state'condition with condenser 42 line reasonably steady state ofcharge before each new =timingcycle; and more important is the practicallimitation that the high intensity lighting unit 22 should not be calledupon tooperate more frequently than is necessary. For presentlypractical designs of adequately powerful .units, one flash per second isas frequent as should be depended upon.

-It is possible for the front wheels of a second vehicle to engage hose14 before the rear wheels of the first vehicle have reached hose 16; andthis would suppress operation oftthe timer irrespective of whether thatfirst wehicle were speeding. Thus if hoses 14 and 16 were :separated by20 feet (corresponding approximately to the maximumepacing between axlesof a trailer-truck) it would be possible for cars separated by less thanfeet from bumper to bumper to be so close to each other as to :suppressdetection of the first vehicle if it were speeding. :Suchcloseness ismost improbable at highway traflic speeds. However, the controllingconsideration is that the escape of an occasional speeder is of minorconcern so long asthesystem prevents charging an innocent driverwithspeeding.

It is possible for two vehicles to travel so close to each,

:speeder is of secondary concern so long as the system does not operatewrongly to charge the innocent with speeding.

A range of equivalents .for pneumatic hose-operated switches willbeapparent to those skilled in the art. Without limitation, it isevident that normally separated con- .ductors carried in a hose with onelying above the other can be used to complete a circuit directly withoutreliance I on pneumatic pressure and pneumatically operated .switchesfSuch devices have the special advantage of being precisely localized soas to make possible the accurate measurement of speed even were theseparation between hoses 16 and 18 somewhat less than the illustraftivefour feet suggested above. Thus two separate electrical impedance orproximity detectors and the like .appear to be of limited value in theembodiment of Figure 1 as substitutes for hoses to and 1,3.

In Figure 2 there is shown an alternative form of systemmeeting therequirements detailed in connection with the description in Figure 1without relying upon the pneurnaticwform of hose and without relyingupon the wheel .Counter type of vehicle rear detector. Where like parts.are used in Figure 2 as appear in Figure 1, like numerals .are used,prefaced bythe numeral 1' so as to represent the lOO-series numerals.Their description and operation will not be repeated in detail sincethis will be understood- "from the description of Figure 1.

Referring to Figure 2, it is seen that pairs of Wires 116a and 118a arestretched across the trafi'ic lane in substitution for the pneumatic'hosesof Figure 1. Each pair of "wires is normaliy resiliently spacedapart but is actuated After the rear of vehicle 119 has passed the reardetector 114, timer Starting detector 116a can become effective toinitiate the timing operationof unit .136 which, as injFigure 1, may ,bea monostable ,multi-vibrator or flip-flop. Unit 156 should be understoodas embodying suitable'control-signal generation means corresponding toelements .24 to 32,

inclusive, in Figure 1. ,Normally closed contacts will be open when avehicle is in proximity to detector 114.

the input control for timer 136 extends through contacts Normally opencontacts 140];

116a and 50 in series. are seen to be connected in series with contacts118a to energize camera tripper 120a if the wheels strike contact 118awhile contacts 14012 are still closed. It will be understood that inFigure 2 the same camera and strobe lighting installation is involved asin Figure 1 directed at the rear of the vehicle as it passespressure-actuated contacts 118a, but the showing of those elements isomitted as unnecessary to proper understanding.

The time suppressing control in Figure 2 which 1r,e places the countersof Figure l involve a wire 114 that is connected to an impedancedetector 52. This may take a wide variety of forms. Thus wire 114 may bean antenna connected to an oscillator that is readily disturbed by thepresence of a vehicle above it as in proximity fuse and mine detectorapplications, or the element may simply represent an upwardly directedphotocell whose activation is obtained from the sky, obscured so long.as a vehicle is travelling above it. However, as illustrated, element114 is a wire constituting one element of a capacitive impedance betweenthat wire and one of the wires 116a. That capacitive impedance issubstantially reduced so long as a vehicle is in proximity to both. Whenthe rear of the vehicle has left wire 114 and the axle is approachingwire 116a, the normal capacitance may be essentially restored. Thiscapacitance is represented by the dotted terminal capacitors 115. Thecapacitance is greatest when a vehicleis in proximity to both wires andit is quickly reduced to approximately the same as prevails when novehicle is present as soon as the rear of the vehicle passes wire 114appreciably.

The capacitance is measured by a purely illustrative capacitancebridgeinvolving a condenser .54 that approximately equals the capacitancebetween wires 151.4 and 116a when no vehicle is' present; a pair ofmatched resistors 56; an alternating current signal source 57 con nectedbetween one diagonally opposite pair of bridge terminals, and anunbalance amplifier 58 with its relay coil 58a having input connectionsto the other diagonal terminals of the bridge. An isolating condenser 60is interposed between wire 116a and the terminal of the bridge to whichthat wire is to be connected. The condenser is very large compared tothe capacitance between wires 114 and 116;; and is employed so that wire116a may also serve as a timer contact. A second wire may be employedadjacent to the pair of wires 116a,'duplica ting wire 114 at this otherposition near wires 116a,!but the double function arrangementillustrated makes that other arrangement superfluous.

In operation, contacts 50 are normally closed. The

bridge is balanced. This balance is disturbed when the overhanging frontend of a vehicle approaches wires 116a and extends above wire 114. Thiscauses contacts 50 to open so that, thereafter, thefront wheelsengagement with wires 116a is ineffectual to start the timer. .Later,when the rear of the vehicle has appreciably passed wire 114 the bridgeis suiliciently rebalanced so that contacts 50 are closed and the rearwheels are then effective to initiate timer ope-ration. Ultimatephotographic recording of the vehicle rear end follows as described inconnection with Figure 1, under control of timer 136.

A third embodiment of the broad aspects of the invention is illustratedin Figure 3 in which the rear-ofthe-vehicle detector also accomplishesthe function of timer starting. Whilea photocell is illustrated, avariety of impedance-change detectors such as is represented by the wellknown proximity fuse may be substituted. Photocell 214 is connected inseries with a resistor 202 sistor 206. Whenno vehicle is presentphotocell 2'14 ducts maximum current. cell 214 and obscures the skyillumination, the current -in tube 204 drops and a positive pulse isproduced at tion region.

is fully conductive and correspondingly tube 204 convhen a vehiclecovers photothe anode of tube 204. This pulse is transmitted viacondenser 244 (corresponding to condenser 44 in Figure 1) that energizesmonostable flip-flop 236. This flip-flop is insensitive to positivepulses, so that nothing takes place in response to the covering ofphotocell 214. However, when the rear of the vehicle has passedphotocell 214 so that tube 264 once again conducts at maximum current, anegative pulse is transmitted to timer 236 (l ke timer 36) whichinitiates the timing operation. During this timing operation contacts24% (corresponding to contacts 40b in Fig. 1) remain closed so that ifcontacts 218a should close during the timing interval, camera tripper220a would be operated. This occurs when the rear of vehicle 210 nolonger covers photocell 218. This photocell is connected in series withresistor 2-08 between B-plus and B-minus with resistor 2&8 connectedbetween the grid of triode 211 and B-minus. So long as the car coversphotocell 218, tube 211 remains non-conducting (or conducting a nominalcurrent) and relay 213a has 'open contacts. However, when the rear ofthe vehicle has passed photocell 218, tube 211 conducts heavy current toenergize relay 218a and close its contacts. Only if the closing occurswithin the time that contacts 24% are closed will camera 22th: operate.If contacts 24tlb open before contacts 218a close, it is establishedthat the vehicle has travelled at the permissible rate and should not bephotographed.

It the rear of the vehicle has passed detector 214 before the front hasreached detector 218, contacts 24% and 218a will both be closedsimultaneously and the camera will be tripped. The result will be tophotograph the front end of the vehicle from the camera situated aboveand to the rear of the intended framed position of the license plates ofspeeding vehicles. This is a spurious photograph that does not evidencespeeding, and is wasteful but does not result in wrongful chargesagainst the innocent. However to avoid this contingency it is desirableto position photocells within six feet of each other so as to avoid suchspurious operation.

The photocells advantageously incorporate tubes or optical lens systemsto make them sharply directional.

To avoid response to the space between a bumper and a body or between atrailer and the hauling truck, it will be advantageous to aim thephotocell directional system slantwise, as toward the approachingtraific.

Detectors 214 and 218 are illustrated as being photo cells arranged tobe responsive not to the interruption of light occasioned by the entryof the vehicle but rather are arranged to be responsive to therestoration of normal conditions that prevail when no vehicle ispresent, indicating passage or departure of the vehicle from the detec-Other sharply localized object detectors, as magnetometers, apparatusdesigned as mine detectors radiationresistance-change radio detectorsandthe like. These have the advantage that they remain efiective despitethe presence of road dirt that may be somewhat of a problem in the caseof photocells mounted in the road and upwardly directed. However thedirt problem is readily solved by proper mechanical installatiorn'andthe sharply localized property of the photocell is of immense advantageto this problem.

Prominently characteristic of all three embodiments of the broad aspectsof my invention is the feature that the rear of the vehicle initiatestiming. In the forms of Figs. 2 and 3, this may detect the rear of thevehicle physically where a photoelectric or like vehicle-rear detectoris employed. This may respond to the restoration of lighting conditionsprevailing when no vehicle is present, or to the restoration ofcapacitance existing in the system when no vehicle is present, or to therestoration of normal effective antenna resistance in the region of thevehicle-rear detector; or it may be responsive to the rear set of wheelsin particular. The application of localized forms of detectors, e.g. thephotocell, the pressure-actuated switch, the radio-frequency impedancechange detector, all adapt the system to accurate location of thevehicle that is to be accurately framed in the camera field and in thestrobe lighting beam. These localized forms of vehicle detectors,integrated into the elapsed-time type or speed measuring system, enablesspeed measurement in a restricted accurately defined region that helpsto avoid spurious operation of the camera in photographing one slowvehicle in response to another speeding vehicle that may escapeunidentified. In broad concept however, it is not considered beyond thescope of the present invention to employ a localized doppler radar beamor the like for speed measurement without dependence upon elapsed-timesystems of speed measurement.

In each embodiment detailed above, a speed measuring or gaging system iscombined with a detector responsive to the rear of the vehicle. Trippingof the photographic apparatus aimed at the vehicle rear is the jointresult of vehicle-speed gaging and vehicle-rear detection; but in theforegoing embodiments the gaging system is suppressed by thevehicle-rear detector and is initiated into operation by the rearportion of the vehicle.

it is entirely feasible to measure or gage vehicle speed without regardto what part of the vehicle is utilized in that operation. Thus thefamiliar continuous-wave radar speed measurement may depend on responsefrom an uncertain portion of the vehicle; yet an indication of excessspeed may be stored until later when, jointly with detection of thespeeding vehicle rear, the speed gaging and the vehicle-rear detectingdevices may trip the photographic apparatus. Here the speed gaging isnot delayed until the vehicle rear is detected, as in the first threeembodiments. Such a system is detailed below, in which reference is madeto Fig. 4.

In Fig. 4, pneumatic hoses 316 and 318 (employing the 300-seriesnumerals where possible to denote corresponding components in Fig. I)operate pressure-actuated switches 316a and 318a, here responsive to thefront wheels of an approaching vehicle 310. Closing of contacts 316acauses a pulse to be generated by components 324, 326, 323 and 332suitable to trigger timer 336 into operation to close contacts 34012 fora predetermined period of time. The parts of the timer and theiroperation are the same as those of timer 36 in Fig. l and need not berepeated here. Sufiice it to note that the time that contacts 34% remainclosed corresponds to the minimum permissible time it should take aproperly operated vehicle to travel from hose 316 to hose 318.

It might be possible for a second set of wheels to close contacts 316a,and apply a pulse to timer 336 so as to extend the timing interval anderroneously indicate excess speed where a vehicle actually travelled ata reasonable and proper speed. The apparatus of Fig. 4 utilizes avehicle-detector to suppress renewed transmission of pulses to timer335. This detector 352 as illustrated takes the form and operates likethe detector of Fig. 2,

there used to detect the vehicle rear to initiate timer operation andhere used for both the detection of the vehicle rear and for suppressingmultiple pulse trans mission to the timer. This latter function could beomitted it photocells replaced pressure-actuated switches 316a and 313a.Detector 3S2 incorporates normally closed contacts 358b, closed when thebridge is balanced, when the impedance between wires 316i? and 3180 isundisturbed by the presence of a vehicle. When this impedance issufiiciently disturbed to unbalance the bridge, contacts 358k open; andthereafter, so long as a vehicle is present, repeated operation ofcontacts 316a is ineffectual. The positioning of hoses 316 and wires3160 and 3180 9 is adjusted for this result, taking into account theproportions of vehicles to be detected.

'Whentimer 336 holds contacts 134% closed in response to the frontvehicle wheels engaging hose 316, the front wheels may cause contacts318a to close. If the vehicle is traveling at excessive speed, thiswilloccur, whereupon relay 3130' would be energized power supply 318bthrough contacts 349i; and 318a in series. It will be recalled that atthis time, due to bridge unbalance relay 358a is energized. This closescontacts 350 corresponding to contacts'SlB in Fig. 2; but here contacts350 do not initiate timer operation but complete a stick or holdingcircuit for relay 31% once that has been energized by closmg of contacts318a While timer contacts 340!) are closed.

The holding circuit includes supply 318b, contacts 350 and relay holdingcontacts 318d, in series in addition to,

the relay itself. Thus the gaged result of excess speed is stored. V I

The storage continues until the rear of the vehicle has advanced so thatit is in the range of the photographic apparatus previously described.When the impedance between wires 3160 and 3180 has been restoredsufiiciently to rebalance bridge 352, contacts 350 open, deenergizingrelay 3180. Contacts 318e of this relay close, to trigger a pulsegenerator 370 to momentarily energize camera tripper 32th: and, with it,the whole camera an strobe lighting equipment; I I

Renewed opening and closing is requiredbefore renewed camera operationcan ensue; and before this can take place the speedgaging meansincluding elements 316, 318 and 336 must again reveal excessive speed,this indication must be stored and the stored speed indication must becleared by detection of the vehicle rear by device 352 which soresponds. remains closed, repeated operation of contacts318a is ofnoconcern. Operation of contacts 3 18a after timer contacts 34% haveopened is equally ineffectual despite subsequent detection by elements316,318 and 352 of the rear of the vehicle. Thus the vehicle-reardetector and the speed gaging means act jointly to open contacts 318::and thereafter closethose contacts, thereby to energize the cameratripper, but only in response to vehicles speeding at excessive rate.

As a matter of terminology, each of the foregoing embodiments is seen toinclude elements that are disposed for sensing a vehicle in the t'rafliclane approaching the 'field of the camera. Thus, in Fig. 1 elements14-'-14a, "1'616a and 1818a sense the vehicle. In Fig. 2 elements114115116a sense'the vehicle as do elements 116a and 118a individually.In Fig. 3 each of the photocellsconstitute vehicle sensing means. InFig. 4 elements So long as the holding circuit 316316a and 3183.18asense the vehicles as do elements 31603180. Further, each of thevehicle-rear detectors in Eigs. 1-4 are changed toyonecondition by theapproach of a vehi'cle "into sensing range and the vehicle-reardetectors are reversely changed {to another condition uponpassing ofthevehicle, the latter change being utilized herein for controlpurposes. In Fig. 1 a *carupsetting balance of the counters signals itspassing "by restoringthe counters to balance, which restoration,

without more, effects the desired control. In Figs. land 4, theimpedance changes due to acarthat enters the detection zone, andthereverse change is utilized for the desired control, as is true, too, ofphotocell 218 in Fig. 3. The foregoing embodimentsof my inventionarehighly clfectivejn providing photographic evidence against speedingcars, trucks, etc. ,It is especially desirable in some communities wherespeeding trailer trucks .are regarded outstandingly hazardous thatevidence be ob- "tained reliably, irrespective of the length ofthevehicle.

It is especially here that the invention disclosed is irri- -portant.Strobe lighting can be usedin photographing the rear end of a truckwithoutfear of blinding the driver; zan'cliwith such lighting thelicense plates willbe revealed 11) at all times, and shadows often castby 'tailboards and-the like will be eliminated. Strobe lighting iseifective to record sharp pictures because of its inherent brieflighting pulse; and because of its high intensity, comparatively slowcolor film can be used, greatly aiding identification of the licenseplate, particularly as to state of origin.

The foregoing illustrative disclosure of my invention in various aspectsincludes subcombinations that may be readily applied for a variety ofpurposes; and the systems illustrated are manifestly subject to avariety of substitutions and rearrangement. Therefore the appendedclaims should be accorded due latitude of interpretation, consistentwith the spirit and scope of my invention.

What I claim is:

1. A'photographic speedmonitor, including an electrically-actuatedcamera and a strobe lighting device synchronized therewith and directedat a particular re gion in a traific lane, a speed detector havingsensing means disposed to respond to vehicles approaching said region,said speed detector being differently responsive to vehicles travelingabove a predetermined speed and those traveling below that predeterminedspeed, the speeddetector being in control relation to said camera andeffective to actuate said camera in response to vehicles traveling atany speed above said predetermined speed, and vehiclerear detectingmeans controlling said speed detector to suppress operation thereofuntil the respective rear ends of the vehicles approaching such regionhave reached a certain location in said lane adjacent to and in advanceof said particular region, said vehicle-rear detecting means includingvehicle-sensing means in control thereof and disposed to be effective insaid lane in advance of said particular region, said vehicle reardetecting means being changed from one condition while a vehicle ispresent in the region of the sensing means thereof to another conditionas the vehicle passes that sensing region and being thereupon operativeto 'end the suppression of the 1 speed detector operation.

2. A photographic speed monitor, including electrically actuatedphotographic apparatus directed at a particular region in a trafficlane, a speed detector including vehiclesensing means in control thereofand disposed to be ef- 'fective in a zone of that lane at the approachside of and close to said particular region, said speed detector beingdifferently responsive to a vehicle traveling above a predeterminedspeed and to a vehicle traveling slower than that predetermined speed, adetector uniquely responsive to the rear of a vehicle and includingvehiclesensing means in control thereof and disposed to be effective ina' zone of that lane at the approach side of and close to said region,said vehicle-rear detector including means changedin one manner uponapproach of a vehicle to the sensing means thereof, and changed in thereverse manner upon passage of said vehicle and being effectivethereupon to produce control output and actuating means for saidphotographic apparatus rendered operative and controlled by output fromsaid detectors in response to a traveling above a predetermined speedand to a vehicle traveling below that predetermined speed, saidvehiclerear detector responding differently to a vehicle as it enters,and as it departs from the portion of the trafiic lane at which thevehicle-sensing means thereof is efiective, and a camera and strobelighting device directed at the end of said restricted portion of saidlane and being connected in controlled relation to and controlled byboth said vehicle speed detector and said vehicle-rear detector andrendered operative in response to the passing-of a vehiete 11 throughsaid restricted portion of said traflic lane that traveled therethroughabove the predetermined speed.

4.. A photographic speed monitor, including electrically actuatedphotographic apparatus directed at a particular region in a trafficlane, a vehicle speed detector and a vehicle-rear detector disposed tobe effective in a portion of the lane immediately preceding said region,said vehicle speed detector responding in one manner to a vehicletraveling below a predetermined speed and responding in a differentmanner to a vehicle traveling in excess of that speed, said vehicle-reardetector including means responding in one manner upon approach of avehicle thereto and responding in a different manner as that vehicledeparts, and actuating means for said photographic apparatus operativelyconnected to and controlled by both said detectors to cause operation ofsaid apparatus as the result of and immediately after the latterresponses of both of said detectors to a passing vehicle traveling at aspeed in excess of said predetermined speed.

5. Photographic speed monitoring apparatus, including a localizedvehicle speed detector normally inoperative but adapted to be renderedoperative in a confined region along a trafiic lane, a camera connectedto said speed detector for control thereby, said camera being directedat a location in said traflic lane adjacent said confined region andfurther along said lane in the normal direction of traffic, andvehicle-rear detecting means connected in control relation to said speeddetector, said vehicle-rear detecting means including vehicle-responsivemeans, said vehicle-rear detecting means being changed from a first to asecond condition by the proximity of a vehicle to saidvehicle-responsive means and being reversely changed to the firstcondition as the vehicle leaves said vehicle-responsive means, saidnormally inoperative speed detector being coupled to saidvehicle-responsive means and rendered operative by said reverse change.

6. In combination, a camera directed at a particular region in a trafiiclane, and vehicle-responsive control means connected in control relationthereto, said vehicle- .responsive means including vehicle sensing meansinstalled in said lane in advance of said particular region and adjacentthereto and electrical means controlled by said sensing means andchanged from a first condition to a second condition when a vehicle issensed by said sensing means, and said electrical means being reverselychanged to said first condition when the rear of a vehicle passes saidsensing means, said electrical means being adapted to control saidcamera only in response to the latter change.

7. The combination in accordance with claim wherein saidvehicle-responsive means embodies an electrical impedance detector.

8. Apparatus in accordance with claim 5 wherein said vehicleresponsivemeans includes two successive pressure operated switches, countersactuated by said two switches respectively and means effective toinitiate operation of said speed detector as soon as the counteroperated by the second switch registers the same count as the counteroperated by the first switch.

9. Electrically actuated photographic apparatus directed at a particularregion in a trafiic lane, in combination with a speed detector effectivein a zone of the lane to gage speed of a vehicle passing along saidlane, a device uniquely responsive to the rear of the vehicle inproximity to the speed gaging zone, said device includingvehicleresponsive means changed in one manner upon approach of a vehiclethereto and changed reversely upon passage of said vehicle and beingadapted to produce control output as an incident of the latter change,and means jointly controlled by said speed detector and by saidvehicle-rear responsive device to actuate said photographic apparatus atthe moment the rear of a vehicle passing at excess speed reaches saidregion.

10. Apparatus in accordance with claim 9, wherein ,said speed gagingdetector is initiated in operation by the passing vehicle independentlyof said vehicle-rear responsive device, and wherein means is providedfor storing indication of excess speed under control of said speedgaging detector until the rear of the vehicle has reached saidparticular region as evidenced by response of the vehiclerear responsivedevice.

11. Apparatus in accordance with claim 9 wherein sald vehicle responsivedevice embodies an impedance-change detector effective in the trafficlane.

12. A camera and a strobe lighting unit synchronized therewith and bothdirected obliquely at the rear of vehicles passing a detection region ina traffic lane, first and second photocells disposed in succession alongthe lane in the detection region, a timer initiated in operation inresponse to the change in the first photocell only from dark to light,and camera tripping means jointly controlled by said timer and by saidsecond photocell, said camera tripping means being responsive to saidsecond photocell for such control only upon change from dark to light.

13. An electrically actuated camera directed at a particular region in atraffic lane, in combination with means for actuating said camera, andmeans controlling said camera actuating means, said controlling meansincluding a pair of pressure-actuated switches in said lane ahead ofsaid region with respect to the normal direction of vehicles travellingalong said trafiic lane, said pressure-actuated switches being locatedat positions spaced apart along the lane by a distance greater'than themaximum spacing between the axles of the vehicles in said lane to bephotographed, a pair of counters connected to said switches,respectively, to be advanced thereby, and said controlling team havingmeans to detect coincidence of the counters and said controlling means,said means to detect coincidence being connected in control relation tosaid camera actuating means.

14. In combination, means for detecting vehicles traveling at excessivespeed through a limited region of a traffic lane, a camera operativelyconnected to said means and controlled thereby and directed at alocation in said traffic lane beyond said limited region, control meansconnected in control relation to said speed detecting means includingvehicle responsive means, said control means being changed from a firstto a second condition by proximity of a vehicle to said vehicleresponsive means and reversely change to the first condition upondeparture of the vehicle from said proximity, said control means beingarranged to render said speed detecting means operative in response tosaid reverse change.

15. In combination, a camera directed at a location in a traffic lane,actuating means connected in control relation to said camera selectivelyresponsive to vehicles in ,saidllane to cause operation of the camera tophotograph only certain vehicles reaching said location, saidactuatingfmeans including a speed detector, and control .means connectedin control relation to actuating means including'mans responsive to boththe front and the rear of each vehicle traveling along said lane, saidcontrol means embodying a portion changed from a first condition to asecond condition by response of said vehicle front and rear responsivemeans to the front of a vehicle and said portion being changed reverselyto said first condition by response of said vehicle front and rearresponsive means to therear of a vehicle, said control means beingthereupon effective to enable operation of said selectively responsivecamera actuating means in dependence upon determination by said speeddetector of excess speed of 16. A photographic speed monitorin-accordance with claim 2, including at least one electricalvehicle-responsive element installed in the trafiic lane and connectedas a sensing element in common to. both the vehicle-sensing means of thespeeddetector and the-vehicle-sensing means .of the vehicle-reardetector.

p 17. Apparatus in accordance with claim 15, wherein 13 said vehiclefront and rear responsive means includes a pair of wheel-pressureactuated switches spaced apart along said lane by a distance largerthanthat of the frontto-rear separation of wheels of vehicles to bephotographed.

18. Apparatus in accordance with claim 17 wherein said portion of saidcontrol means includes a pair of counters responsive respectively tosaid wheel-pressure actuated switches, and comparison means connected tosaid counters and signalling equal advance of the counters for enablingoperation of said selectively responsive camera-actuating means.

19. Apparatus in accordance with claim 18, wherein said last named meansincludes an elapsed-time gating device initiated in operation by saidcomparison means and an additional pressure-actuated switch connected toand operative for producing a final control signal to said thereto ascompared to the impedance magnitude thereof in the absence of a vehicle,and wherein said electrical means includes an impedance measuring bridgehaving said electrical. conductors connected thereto as an arm thereof,and wherein said first condition is bridge balance and said secondcondition is bridge unbalance.

21. The combination'in accordance with claim 6, wherein said vehiclesensing means includes a photocell connected to said electrical meansand is installed in the traflic lane so as to be exposed to light fromabove, and wherein said electrical means is in said first condition whensaid photocell is unobstructed and is changed to said second conditionwhen said photocell is obstructed by. a vehicle.

elapsed time gating device, said additional switch being disposedbetween said location in said trafiic lane and said pair ofpressure-actuated switches.

20. The combination in accordance with claim 6 where- 7 References Citedin the file of this patent UNITED STATES PATENTS

